West Germany Published Application No. 3,315,548 discloses a childproof closure for containers, in particular bottles with a threaded inside cap and an outside cap which is axially displaceable relative to the inside cap, a crown of elastic tongues being located at the cover plate of one of the caps, and where the elastic tongues are oblique relative to the plane of the cover plate.
In this known closure, both when closing and opening, both a torque and an axial force directed toward the mouth must be exerted. For that purpose a coupling is provided between a threaded inner cap and an outer cap, comprising at least one elastically flexible element which is inactive in the rest position and is deformed only when subject to an axial force directed from the outer cap toward the threaded cap. In the process there is enough friction between the two caps so that the outer caps can drag along the inner one. As shown by FIGS. 8 or 9 of West German Published Application No. 3,315,548 the coupling element may be a hollow frustrum of a cone present at the inner cap and directed toward the annular corner between the surface and the cover plate of the outer cap. When the outer cap is pressed against the inner cap, the frustoconical membrane is bent against the cover plate of the inner cap and is clamped against the annular projection or the inside wall of the inner cap surface, whereby a torque then may be applied from the outer cap to the inner one.
In the rest position, the elastic membrane ensures that the cover plates of the inner and outer caps are pushed apart so that the outer cap can freely rotate relative to the inner one.
In every case, the elastic membrane is so deformed by an axial force exerted by the outer cap on the inner one that a friction lock takes place which is adequate to drag along the inner cap in either direction of screwing. Accordingly the outer cap must be foced axially against the inner cap both when opening the container (which is required for child safety) but also when tightening it, which is irrelevant to child safety while however demanding special procedures in sealing machines.